There is considerable interest in the identification, isolation and generation of human stem and progenitor cells. Stem cells are totipotential or pluripotential precursor cells capable of generating a variety of mature cell lineages, and precursor cells are cells capable of generating cells of specific cell lineages. These abilities serve as the basis for the cellular differentiation and specialization necessary for organ and tissue development.
Recent success at transplanting stem and progenitor cells have provided new clinical tools to reconstitute and/or supplement bone marrow after myeloablation due to disease, exposure to toxic chemical and/or radiation. Further evidence exists that demonstrates that stem cells can be employed to repopulate many, if not all, tissues and restore physiologic and anatomic functionality. The application of stem cells in tissue engineering, gene therapy delivery and cell therapeutics is also advancing rapidly.
Many different types of mammalian and progenitor stem cells have been characterized. For example, embryonic stem cells, embryonic germ cells, adult stem cells or committed stem cells or progenitor cells are known. Certain stem cells have not only been isolated and characterized but have also been cultured under conditions to allow differentiation to a limited extent. However, a basic problem remains; that is, it has been difficult to control or regulate the differentiation of stem cells and progenitor cells, such as hematopoietic progenitor cells. Presently, existing methods of modulating the differentiation of these cells are crude and unregulatable, such that the cells differentiate into unwanted cell types, at unwanted times. Moreover, the yield of the product cells is typically low.
Furthermore, obtaining sufficient numbers of human stem cells for therapeutic or research purposes is problematic. Isolation of normally occurring populations of stem or progenitor cells in adult tissues has been technically difficult and costly, due, in part, to the limited quantity of stem or progenitor cells found in blood or tissue, and the significant discomfort involved in obtaining bone marrow aspirates. In general, harvesting of stem or progenitor cells from alternative sources in adequate amounts for therapeutic and research purposes is generally laborious, involving, e.g., harvesting of cells or tissues from a donor subject or patient, culturing and/or propagation of cells in vitro, dissection, etc. With respect to stem cells in particular, procurement of these cells from embryos or fetal tissue, including abortuses, has raised religious and ethical concerns. The widely held belief that the human embryo and fetus constitute independent life has prompted governmental restrictions on the use of such sources for all purposes, including medical research. Alternative sources that do not require the use of cells procured from embryonic or fetal tissue are therefore desired for further progress in the use of stem cells clinically. There are, however, few viable alternative sources of stem or progenitor cells, particularly human stem or progenitor cells, and thus the supply is limited.
Hu et at (WO 00/73421 entitled “Methods of isolation, cryopreservation, and therapeutic use of human amniotic epithelial cells,” published Dec. 7, 2000) discloses human amniotic epithelial cells derived from placenta at delivery that are isolated, cultured, cryopreserved for future use, or induced to differentiate. According to Hu et al., a placenta is harvested immediately after delivery and the amniotic membrane separated from the chorion, e.g., by dissection. Amniotic epithelial cells are isolated from the amniotic membrane according to standard cell isolation techniques. The disclosed cells can be cultured in various media, expanded in culture, cryopreserved, or induced to differentiate. Hu et al. discloses that amniotic epithelial cells are multipotential (and possibly pluripotential), and can differentiate into epithelial tissues such as corneal surface epithelium or vaginal epithelium. The drawback of such methods, however, is that they are labor-intensive and the yield of stem cells is very low.
Currently available methods for the ex vivo expansion of cell populations are also labor-intensive. For example, Emerson et al. (Emerson et al., U.S. Pat. No. 6,326,198 entitled “Methods and compositions for the ex vivo replication of stem cells, for the optimization of hematopoietic progenitor cell cultures, and for increasing the metabolism, GM-CSF secretion and/or IL-6 secretion of human stromal cells”, issued Dec. 4, 2001); discloses methods, and culture media conditions for ex vivo culturing of human stem cell division and/or the optimization of human hematopoietic progenitor stem cells. According to the disclosed methods, human stem cells or progenitor cells derived from bone marrow are cultured in a liquid culture medium that is replaced, preferably perfused, either continuously or periodically, at a rate of 1 ml of medium per ml of culture per about 24 to about 48 hour period. Metabolic products are removed and depleted nutrients replenished while maintaining the culture under physiologically acceptable conditions.
Kraus et al. (Kraus et al, U.S. Pat. No. 6,338,942, entitled “Selective expansion of target cell populations,” issued Jan. 15, 2002) discloses that a predetermined target population of cells may be selectively expanded by introducing a starting sample of cells from cord blood or peripheral blood into a growth medium, causing cells of the target cell population to divide, and contacting the cells in the growth medium with a selection element comprising binding molecules with specific affinity (such as a monoclonal antibody for CD34) for a predetermined population of cells (such as CD34 cells), so as to select cells of the predetermined target population from other cells in the growth medium.
Rodgers et al. (U.S. Pat. No. 6,335,195 entitled “Method for promoting hematopoietic and mesenchymal cell proliferation and differentiation,” issued Jan. 1, 2002) discloses methods for ex vivo culture of hematopoietic and mesenchymal stem cells and the induction of lineage-specific cell proliferation and differentiation by growth in the presence of angiotensinogen, angiotensin I (AI), AI analogues, AI fragments and analogues thereof, angiotensin II (AII), All analogues, All fragments or analogues thereof or All AT2 type 2 receptor agonists, either alone or in combination with other growth factors and cytokines. The stem cells are derived from bone marrow, peripheral blood or umbilical cord blood. The drawback of such methods, however, is that such ex vivo methods for inducing proliferation and differentiation of stem cells are time-consuming, as discussed above, and also result in low yields of stem cells.
Stem and progenitor cells have the potential to be used in the treatment of a variety of disorders, including malignancies, inborn errors of metabolism, hemoglobinopathies, and immunodeficiencies. One major area of use and research involving stem cells from cord blood or placenta has been the use of such cells to generate small quantities of cells for bone marrow and other related transplantations. However, to date, no one has described a method of producing substantial numbers of stem or progenitor cells, such as human CD34+ or CD133+ progenitor cells. Large numbers of the latter cells, in particular, would facilitate treatment methods using progenitor cells. The methods of the invention disclosed herein addresses this need.
Retinoids, such as vitamin A and retinoic acid (RA), have been known to affect differentiation of stem cells. For example, retinoic acid has been shown to inhibit proliferation of abnormally committed (chronic myelogenous leukemia) hematopoietic stem cells (Nadkarni et al. 1984, Tumori 70:503-505) and to induce differentiation and loss of self-renewal potential in promyelocytic leukemia cells (Melchner et al., 1985, Blood 66(6): 1469-1472). Retinoic acid has also been shown to induce differentiation of neurons from embryonic stem cells and to repress spontaneous mesodermal differentiation (Slager et al., Dev. Genet. 1993; 14(3):212-24, Ray et al., 1997, J. Biol. Chem. 272(30): 18702-18708). Retinoic acid has further been shown to induce differentiation of transformed germ cell precursors (Damjanov et al., 1993, Labor. Investig. 68(2):220-232), placental cell precursors (Yan et al., 2001, Devel. Biol. 235: 422-432), and endothelial cell precursors (Hatzopoulos et al., 1998, Development 125: 1457-1468). The effect of retinoids on differentiation, however, has yet to be completely understood such that it could be used as a regulatable means of controlling differentiation of stem cells.
The effects of folic acid analogues, such as aminopterin and amethopterin (methotrexate), on the differentiation of hematopoietic stem cells has been studied. Folic acid analogues are used as chemotherapeutic agents in acute lymphoblastic anemias and other blood proliferation disorders and cancers, and have been shown to effect differentiation of stem cells by killing off certain populations of stem cells (DeLoia et al., 1998, Human Reproduction 13(4): 1063-1069), and thus, would not be an effective tool for regulating differentiation of large quantities of stem cells for administration to a patient.
Several cytokines, such as IL-1, IL-2, IL-3, IL-6, IL-7, IL-11, as well as proteins such as erythropoietin, Kit ligand, M-CSF and GM-CSF have also been shown to direct differentiation of stem cells into specific cell types in the hematopoietic lineage (Dushnik-Levinson et al., 1995, Biol. Neonate 67:77-83), however, these processes are not well understood and still remain too crude and imprecise to allow for a regulatable means of controlling differentiation of stem cells.
To date, no one has described the use of compounds, such as the immunomodulatory compounds discussed below, in the differentiation of stem cells or precursor cells. In particular, no one has demonstrated the use of such compounds to modulate the differentiation of progenitor cells, such as CD34+ progenitor cells, away from a dendritic cell lineage, a capability useful in encouraging transplant immune tolerance. Likewise, no one has described the use of the compounds described herein to expand the progenitor cell populations so as to produce a pharmaceutical composition containing such cells. Such expanded progenitor cell cultures would be useful in the treatment of graft-versus-host disease and the development of immune tolerance. Because control over stem and precursor cell differentiation can produce cell populations that are therapeutically useful, there is a need for the ability to control and regulate the differentiation of cells of myeloid dendritic cell lineage, or early progenitor cells, such as human CD34+ or CD133+ progenitor cells, for the controlled production of dendritic cells and/or granulocytes.